Most studies on placebo mechanisms rely on Expectancy Theory, which suggests that conceptual expectations can bring about physiological change. However, the exact processes underlying this effect remain unclear. Perceptual Symbol Systems (PSS) Theory, grounded in Embodied Cognition Theory, offers a more specific explanation: mental representations grounded in sensory-motor systems may directly evoke bodily responses. This study tested whether embodied primes, based on PSS Theory, elicit stronger placebo responses than traditional expectancy-based suggestions. Using a within-subjects design, 71 university students underwent a cold pressure task under three conditions: (1) verbal suggestion of an analgesic cream, (2) visual priming with a photo of a person looking upward, and (3) combined visual-motor priming, where participants also looked upward themselves. The placebo response was measured by changes in pain intensity and heart rate. Results showed that both embodied conditions (visual and visual-motor priming) produced stronger placebo responses than the verbal suggestion condition, as indicated by lower pain intensity and reduced heart rate (F(2,140)=5.83; p<.01). However, the difference between the two embodied conditions was not statistically significant in terms of pain ratings. Notably, visual-motor priming led to a greater reduction in heart rate than visual priming alone (F(6,330)=1.99; p=.06), suggesting a subtle additive effect of motor engagement. These findings support the role of unconscious embodied processes—specifically, perceptual and motor representations—in modulating placebo responses. They offer a promising direction for understanding how non-verbal bodily cues may influence the complex perception of pain.
